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Interconversion between charge and spin through spin-orbit coupling at a heavy metal (HM)/ferromagnet (FM) interface plays a key role in determining the amplitude of spin Hall magnetoresistance (SMR), which might maximally facilitate its applications in novel electronics. In this study, annealed NiFe films grown on MgO (100) substrates capped with Pt and Ta are reported to exhibit a maximum SMR. When the measuring temperature is reduced, the SMR rises and is significantly larger in crystalline NiFe than in amorphous NiFe. Another physical process for the negative SMR in Ta(

Exposome has become the hotspot of next-generation health studies. To date, there is no available effective platform to standardize the analysis of exposomic data. In this study, we aim to propose one new framework of exposomic analysis and build up one novel integrated platform “ExposomeX” to expediate the discovery of the “Exposure-Biology-Disease” nexus. We have developed 13 standardized modules to accomplish six major functions including statistical learning (E-STAT), exposome database search (E-DB), mass spectrometry data processing (E-MS), meta-analysis (E-META), biological link via pathway integration and protein-protein interaction (E-BIO) and data visualization (E-VIZ). Using ExposomeX, we can effectively analyze the multiple-dimensional exposomics data and investigate the “Exposure-Biology-Disease” nexus by exploring mediation and interaction effects, understanding statistical and biological mechanisms, strengthening prediction performance, and automatically conducting meta-analysis based on well-established literature databases. The performance of ExposomeX has been well validated by re-analyzing two previous multi-omics studies. Additionally, ExposomeX can efficiently help discover new associations, as well as relevant in-depth biological pathways via protein-protein interaction and gene ontology network analysis. In sum, we have proposed a novel framework for standardized exposomic analysis, which can be accessed using both R and online interactive platform (http://www.exposomex.cn/).

Realization of functional flexible artificial synapse is a significant step toward neuromorphic computing. Herein, a flexible artificial synapse based on ferroelectric tunnel junctions (FTJs) is demonstrated, using BiFeO3 (BFO) thin film as the functional layer. The inorganic single crystalline FTJs grown on rigid perovskite substrates at high temperatures are integrated with the flexible plastic substrates, by using the water-soluble Sr3Al2O6 (SAO) as the sacrificial layer and the following transfer. The transferred freestanding BFO thin film exhibits excellent ferroelectric properties. Moreover, the memristive properties and the brain-like synaptic learning performance of the flexible FTJs are investigated. The results show that multilevel resistance states were maintained well of the flexible artificial synapse, together with their stable synaptic learning properties. Our work indicates the promising opportunity of ferroelectric thin film based flexible synapse used in the future neuromorphic computing system.

Current-induced spin-orbit torque (SOT) switching of magnetization has attracted great interest due to its potential application in magnetic memory devices, which offer low-energy consumption and high-speed writing. However, most of the SOT studies on perpendicularly magnetized anisotropy (PMA) magnets have been limited to heterostructures with interfacial PMA and poor thermal stability. Here, we experimentally demonstrate a SOT magnetization switching for a ferrimagnetic D022-Mn3Ge film with high bulk PMA and robust thermal stability factor under a critical current density of 6.6 × 1011 A m-2 through the spin Hall effect of an adjacent capping Pt and a buffer Cr layer. A large effective damping-like SOT efficiency of 2.37 mT/1010 A m-2 is determined using harmonic measurements in the structure. The effect of the double-spin source layers and the negative-exchange interaction of the ferrimagnet may explain the large SOT efficiency and the manifested magnetization switching of Mn3Ge. Our findings demonstrate that D022-Mn3Ge is a promising candidate for application in high-density SOT magnetic random-access memory devices.

Antiferromagnetic (AFM) materials have attracted wide attention in spin-orbit torque (SOT)-based spintronic due to its abundant spin-dependent properties and unique advantage of immunity against external field perturbations. To act as the charge-to-spin conversion source in energy-saving spintronic devices, it is of great importance for the AFM material to possess a large spin torque efficiency (ξDL). In this work, using the spin torque ferromagnetic resonance (ST-FMR) technique and a Mn2Au/NiFe(Py) bilayer system, we systemically study the ξDL of AFM Mn2Au films with different crystal structures. Compared with polycrystalline Mn2Au with effective ξDL < 0.051, we show a much larger ξDL of ~0.333 in single-crystal Mn2Au, which arises from the large spin Hall conductivity instead of electrical resistivity. Moreover, with a further contribution of interfacial effects, the effective ξDL of single-crystalline Mn2Au/Py system increases to 0.731, which is more than two times larger than the value of ∼0.22 reported for the Mn2Au/CoFeB system. By utilizing the large ξDL of Mn2Au in a perpendicularly magnetized MnGa/Mn2Au system, energy-efficient deterministic magnetization switching with a current density at ~106 A cm−2 is achieved. Our results reveal a significant potential of Mn2Au as an efficient SOT source and shed light on its application in future AFM material-based SOT integration technology.

Van der Waals materials are attracting great attention in the field of spintronics due to their novel physical properties. For example, they are utilized as spin-current generating materials in spin-orbit torque (SOT) devices, which offers an electrical way to control the magnetic state and is promising for future low-power electronics. However, SOTs have mostly been demonstrated in vdW materials with strong spin-orbit coupling (SOC). Here, the observation of a current-induced SOT in the h-BN/SrRuO

Two-dimensional electron gas (2DEG) at the interface between two insulating perovskite oxides has attracted much interest for both fundamental physics and potential applications. Here, we report the discovery of a new 2DEG formed at the interface between spinel MgAl

Flexoelectricity induced by the strain gradient is attracting much attention due to its potential applications in electronic devices. Here, by combining a tunable flexoelectric effect and the ferroelectric photovoltaic effect, we demonstrate the continuous tunability of photoconductance in BiFeO3 films. The BiFeO3 film epitaxially grown on SrTiO3 is transferred to a flexible substrate by dissolving a sacrificing layer. The tunable flexoelectricity is achieved by bending the flexible substrate which induces a nonuniform lattice distortion in BiFeO3 and thus influences the inversion asymmetry of the film. Multilevel conductance is thus realized through the coupling between flexoelectric and ferroelectric photovoltaic effect in freestanding BiFeO3. The strain gradient induced multilevel photoconductance shows very good reproducibility by bending the flexible BiFeO3 device. This control strategy offers an alternative degree of freedom to tailor the physical properties of flexible devices and thus provides a compelling toolbox for flexible materials in a wide range of applications., Previous methods to generate strain gradient and flexoelectricity are limited to a localized effect or cannot be tuned continuously. Here, the authors achieve macroscale continuously controllable strain gradient in freestanding ferroelectric thin film. Multilevel photoconductance in BiFeO3 films can be achieved by coupling between the flexoelectric and ferroelectric photovoltaic effect.

Van der Waals antiferromagnets (AFMs) provide a two-dimensional (2D) platform for spintronic devices with exceptional properties. However, the electric transport features of the magnetic order of van der Waals AFM influenced by different field directions and amplitudes has not been demonstrated systematically. In this letter, we investigate the magnetic texture of the exfoliated van der Waals FePS3, a uniaxial AFM with perpendicular anisotropy, detected by the spin Hall magnetoresistance (SMR). Magnetic field- and temperature- dependent longitudinal magnetoresistance measurements in three orthogonal directions for the exfoliated FePS3/Pt nanostructures are conducted. The modulations in the SMR signal enable the separation of two contributions to the SMR, one of which corresponds to the negative signature of AFM SMR caused by in-plane field rotations, and the other of which is caused by canted spins in perpendicular AFM order. Our findings offer great guidance for further research and investigation using SMR approach of the magnetic texture in van der Waals AFMs.

All-electric switching of perpendicular magnetization is a prerequisite for the integration of fast, high-density, and low-power magnetic memories and magnetic logic devices into electric circuits. To date, the field-free spin-orbit torque (SOT) switching of perpendicular magnetization has been observed in SOT bilayer and trilayer systems through various asymmetric designs, which mainly aim to break the mirror symmetry. Here, we report that the perpendicular magnetization of CoxPt100-x single layers within a special composition range (20

To realize high-speed nonvolatile magnetic memory with low energy consumption, electric switching of perpendicular magnetization by spin-orbit torque in the heavy metal/ferromagnetic (HM/FM) structure has recently attracted intensive attention. Conventionally, an external in-plane magnetic field for breaking the symmetry is required for achieving electric switching of perpendicular magnetization. However, electric switching without external field is the prerequisite for the integration of magnetic functionality into the integrated circuit devices. Here, we propose a new method of utilizing a W wedge in the Pt/W/FM structure to induce a spin current gradient, which can result in an in-plane equivalent field along the wedge thickness gradient direction. We experimentally demonstrate the deterministic magnetization switching of perpendicular Co/Ni multilayers without external magnetic field when the electric current is along the wedge thickness gradient direction. Our findings shed light on free field electric switching of magnetization by a new physical parameter-an asymmetric spin current induced by a bilayer wedge structure.

The Rashba effect plays important roles in emerging quantum materials physics and potential spintronic applications, entailing both the spin orbit interaction (SOI) and broken inversion symmetry. In this work, we devise asymmetric oxide heterostructures of LaAlO3//SrTiO3/LaAlO3 (LAO//STO/LAO) to study the Rashba effect in STO with an initial centrosymmetric structure, and broken inversion symmetry is created by the inequivalent bottom and top interfaces due to their opposite polar discontinuities. Furthermore, we report the observation of a transition from the cubic Rashba effect to the coexistence of linear and cubic Rashba effects in the oxide heterostructures, which is controlled by the filling of Ti orbitals. Such asymmetric oxide heterostructures with initially centrosymmetric materials provide a general strategy for tuning the Rashba SOI in artificial quantum materials., The two-dimensional electron gases that form at LaAlO3/SrTiO3 heterostructure interfaces feature strong spin-orbit interactions, leading to proposed spintronic applications. Lin et al. show that the design of asymmetric heterostructures enables the Rashba spin-orbit interaction to be tuned between two regimes.

Owing to the intriguing physical properties and significant spintronic applications, magnetic skyrmions have recently drawn intensive attention. Particularly, the skyrmion-based non-volatile memory (Sky-NVM) devices promise to be spintronic building blocks with high efficiency. However, tailoring Sky-NVM to achieve an energy-efficient and reliable operation in a synthetic, CMOS compatible, and magnetic-field-free integration is a challenging issue. Here, we report a new type of compact Sky-NVM with tailored skyrmion motion dynamics via in-plane strain gradient engineering. The skyrmion motion is merely driven by an in-plane electric field utilizing the magnetoelectric coupling effect, and the programmable switching is realized by gate biasing the potential barrier height via a voltage-controlled magnetic anisotropy. The proposed device is CMOS process compatible, and the comprehensive micromagnetic simulation results demonstrate that by applying a 0.3 V in-plane voltage combined with −0.17 V gate voltage, its write latency and the energy consumption reach 5.85 ns and 4.77 aJ/bit, respectively, superior to the state-of-the-art counterparts. Our work paves a new path toward ultra-low-power spintronic memory devices.

The magnetic Weyl fermion originates from the time reversal symmetry (TRS)-breaking in magnetic crystalline structures, where the topology and magnetism entangle with each other. Therefore, the magnetic Weyl fermion is expected to be effectively tuned by the magnetic field and electrical field, which holds promise for future topologically protected electronics. However, the electrical field control of the magnetic Weyl fermion has rarely been reported, which is prevented by the limited number of identified magnetic Weyl solids. Here, the electric field control of the magnetic Weyl fermion is demonstrated in an epitaxial SrRuO

Current-induced spin-orbit torque (SOT) switching of magnetization has attracted great interest due to its potential application in magnetic memory devices, which offer low-energy consumption and high-speed writing. However, most of the SOT studies on perpendicularly magnetized anisotropy (PMA) magnets have been limited to heterostructures with interfacial PMA and poor thermal stability. Here, we experimentally demonstrate a SOT magnetization switching for a ferrimagnetic D0

Spin-orbit torque (SOT), which arises from the spin-orbit coupling of conduction electrons, is believed to be the key route for developing low-power, high-speed, and nonvolatile memory devices. Despite the theoretical prediction of pronounced Berry phase curvatures in certain transition-metal perovskite oxides, which lead to considerable intrinsic spin Hall conductivity, SOT from this class of materials has rarely been reported until recently. Here, the SOT generated by epitaxial SrRuO

Interface-engineered electron or hole tunneling controls tunneling electroresistance in ferroelectric tunnel junctions., Although the phenomenon of tunneling has been known since the advent of quantum mechanics, it continues to enrich our understanding of many fields of science. Commonly, this effect is described in terms of electrons traversing the potential barrier that exceeds their kinetic energy due to the wave nature of electrons. This picture of electron tunneling fails, however, for tunnel junctions, where the Fermi energy lies sufficiently close to the insulator valence band, in which case, hole tunneling dominates. We demonstrate the deterministic control of electron and hole tunneling in interface-engineered Pt/BaTiO3/La0.7Sr0.3MnO3 ferroelectric tunnel junctions by reversal of tunneling electroresistance. Our electrical measurements, electron microscopy and spectroscopy characterization, and theoretical modeling unambiguously point out to electron or hole tunneling regimes depending on interface termination. The interface control of the tunneling regime offers designed functionalities of electronic devices.

This paper uses event study based on the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) model to study the impact of the COVID-19 outbreak on China’s financial market. It finds that the pandemic had an overall significant and negative impact on the stock prices of firms listed on SSE, SZSE and ChiNext. However, such impact appeared to be heterogeneous across industries, affecting listed firms in industries such as pharmaceutical and telecommunications positively, but those in services industries such as accommodation, catering, and commercial services negatively. Apparently, a crisis for some had been an opportunity for others. In addition, this paper seeks to understand the micro mechanism behind the heterogeneity of pandemic shock from the perspective of firms’ financial position. It finds that listed firms with higher debt level were hit harder, whereas those with more net cash flow had displayed higher resilience against the blow of the pandemic. However, the opposite pattern is found among those listed on ChiNext and in industries severely devastated by the pandemic. These findings have policy implications in terms of preventing systemic financial risks and facilitating recovery during pandemic-induced economic downturns. It also helps investor adjust investment strategies, hedge against risks, and secure gains when the market conditions in general are unfavorable.

We report a large enhancement of the spin-orbit-torque (SOT) efficiency achieved by inserting an ultrathin $\mathrm{Co}$ layer between a single-crystal $\mathrm{Pt}$ layer and an epitaxial ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ layer. We attribute this to the strong interfacial orbital hybridization between $\mathrm{Pt}$ and $\mathrm{Co}$. Another effect of this hybridization is the spin-rotation effect based on the out-of-plane component of the magnetic moment, which explains the observation of out-of-plane torques. Our results offer an effective approach to engineer the SOT in a conventional ferromagnet-heavy metal system, which might provide opportunities for spintronic application.

The ferroelectric switching effect on perpendicular magnetic anisotropy is examined for the case of the BaTiO3/L10-CoFe interface through first-principles calculations of film magnetocrystalline anisotropy energy (MAE), both with the frozen-potential method and the second-order perturbation theory. The ferroelectric switching-MAE relationship is shown to have opposite trends for BaO- and TiO2-terminated interfaces because of the distinct orbital interaction mechanisms predominant in each termination configuration. The ferroelectric switching effect, changes in Fe-O bond lengths, and termination constitute three different contributors to MAE change, each with a different penetration depth into the CoFe film. The top surface CoFe atoms are shown to feature a high density of minority-spin 3dxz states, which could play a role in influencing the ferroelectric switching-MAE relationship in cases where the top surface undergoes modifications.

We report on the efficient spin-orbit torque (SOT) switching in a single ferromagnetic layer induced by a new type of inversion asymmetry, the composition gradient. The SOT of 6- to 60-nm epitaxial FePt thin films with a $L{1}_{0}$ phase is investigated. The magnetization of the FePt single layer can be reversibly switched by applying electrical current with a moderate current density. Different from previously reported SOTs which either decreases with or does not change with the film thickness, the SOT in FePt increases with the film thickness. We found the SOT in FePt can be attributed to the composition gradient along the film normal direction. A linear correlation between the SOT and the composition gradient is observed. This Rapid Communication introduces a platform to engineer large SOTs for lower-power spintronics.

We demonstrate an anomalous spin-orbit torque induced by the broken magnetic symmetry in the antiferromagnet IrMn. We study the magnetic structure of three phases of IrMn thin films using neutron diffraction technique. The magnetic mirror symmetry $\mathcal{M}{}^{\ensuremath{'}}$ is broken laterally in both $\mathrm{L}{1}_{0}\text{\ensuremath{-}}\mathrm{IrMn}$ and $\mathrm{L}{1}_{2}\text{\ensuremath{-}}\mathrm{IrM}{\mathrm{n}}_{3}$ but not $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{IrM}{\mathrm{n}}_{3}$. We observe an out-of-plane dampinglike spin-orbit torque in both $\mathrm{L}{1}_{0}\text{\ensuremath{-}}\mathrm{IrMn}$/permalloy and $\mathrm{L}{1}_{2}\text{\ensuremath{-}}\mathrm{IrM}{\mathrm{n}}_{3}$/permalloy bilayers but not in $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{IrM}{\mathrm{n}}_{3}$/permalloy. This is consistent with both the symmetry analysis on the effects of a broken $\mathcal{M}{}^{\ensuremath{'}}$ on spin-orbit torque and the theoretical predictions of the spin Hall effect and the Rashba-Edelstein effect. In addition, the measured spin-orbit torque efficiencies are 0.61 \ifmmode\pm\else\textpm\fi{} 0.01, 1.01 \ifmmode\pm\else\textpm\fi{} 0.03, and 0.80 \ifmmode\pm\else\textpm\fi{} 0.01 for the $\mathrm{L}{1}_{0},\mathrm{L}{1}_{2}$, and \ensuremath{\gamma} phases, respectively. Our work highlights the critical roles of the magnetic asymmetry in spin-orbit torque generation.

Heterostructures made of strongly correlated oxides host various fundamentally interesting and potentially useful emergent phenomena. ${(\mathrm{LaMn}{\mathrm{O}}_{3})}_{n}/{{(\mathrm{SrMn}{\mathrm{O}}_{3})}_{n}}_{\ensuremath{-}1}$ superlattices that consist of an $A$-type antiferromagnetic insulator $\mathrm{LaMn}{\mathrm{O}}_{3}$ and a $G$-type antiferromagnetic insulator $\mathrm{SrMn}{\mathrm{O}}_{3}$ were investigated in this work. Several very intriguing effects were observed in such superlattices that include (1) the coexistence of a strong exchange bias effect and a giant vertical magnetization shift in superlattices with intermediate periods, (2) an insulator-to-metal transition associated with a change in the superlattice thickness, and (3) a large nontrivial negative magnetoresistance around the insulator-to-metal transition. To understand these phenomena, microscopic preferential orbital occupancy in different superlattices was studied through measurements of x-ray linear dichroism at Mn $L$ edges. This study facilitated the construction of a spin configuration model that takes into account the competition between interfacial ferromagnetism and underlying canted antiferromagnetism in the superlattices and can successfully explain the observed novel magnetic and transport properties. The phase transition and giant vertical magnetization shift phenomena observed in this work offer additional degrees of freedom for applications of antiferromagnetic insulator manganite-based superlattices, enabling novel device concepts.

Current-induced effective magnetic fields offer a new pathway through spin orbit interaction (SOI) to switch magnetization and have recently attracted great interest. In the conventional heavy metal/ferromagnetic metal/oxide (HM/FM/Oxide) structure, significant efforts have been made to study the role of the HM in determining effective magnetic fields. However, very little attention has been paid to the oxide layer and its interface with FM, where the Rashba effect may affect the effective field. In this report, we present a pathway to tune the effective magnetic field by engineering the Rashba effect in a hybrid multiferroic multilayer structure. A ferroelectric oxide of BaTiO3, whose polarizations either up or down are controlled by interface engineering, was introduced into the conventional SOI multilayer with the structure of BaTiO3/CoFeB/Pt. The current-induced effective magnetic fields increase by more than 200% when the ferroelectric polarization of BaTiO3 changes from up to down. The changes in the effective magnetic field are mainly attributed to the different Rashba effective fields induced by the opposite ferroelectric polarizations. Our study offers a new path towards controlling the current-induced effective magnetic field and may pave the way for integrating other functional oxides into the spintronic devices. Combining magnetic materials with oxides offers a route to low-power memories, according to research from scientists in Singapore. Locally switching the magnetization orientation of a permanent magnet is a way of storing binary data. The energy consumption of these magnetic memories is much lower if a local current, rather than an external magnetic field, induces the switch. Current-induced magnetization switching has previously been demonstrated in devices made by layering a heavy metal, a ferromagnetic material, and an oxide material. While many conventional oxide materials have been tried, Jingsheng Chen and Hyunsoo Yang and their colleagues from the National University of Singapore instead used BaTiO3, a ferroelectric oxide which has permanent internal electric fields. They showed that they could increase the current-induced magnetic fields by more than 200% by altering the ferroelectric polarization of the BaTiO3. Over 200% difference of the current-induced effective magnetic field was achieved through engineering the Rashba effect in a hybrid-multiferroic multilayer structure (BaTiO3/CoFeB/Pt), where the polarization of BaTiO3 with either up or down was controlled through interface engineering. Our works offer a new direction towards controlling the current-induced effective magnetic field and may pave the way to integrate other functional oxides into the spintronic devices.

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO3 ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unit-cell-thick BiFeO3 films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO3 films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO3 film is virtually absent, making it a promising candidate for high-density nonvolatile memories., High temperature perpendicular ferroelectricity in nano thin films is crucial for miniaturization of electronic devices. Here the authors show the presence of stable and switchable out-of-plane ferroelectricity in tetragonal BiFeO3 thin films at the two-dimensional limit and 370% tunneling electroresistance in ferroelectric tunnel junctions.

Brain-inspired computing is an emerging field, which intends to extend the capabilities of information technology beyond digital logic. The progress of the field relies on artificial synaptic devices as the building block for brainlike computing systems. Here, we report an electronic synapse based on a ferroelectric tunnel memristor, where its synaptic plasticity learning property can be controlled by nanoscale interface engineering. The effect of the interface engineering on the device performance was studied. Different memristor interfaces lead to an opposite virgin resistance state of the devices. More importantly, nanoscale interface engineering could tune the intrinsic band alignment of the ferroelectric/metal-semiconductor heterostructure over a large range of 1.28 eV, which eventually results in different memristive and spike-timing-dependent plasticity (STDP) properties of the devices. Bidirectional and unidirectional gradual resistance modulation of the devices could therefore be controlled by tuning the band alignment. This study gives useful insights on tuning device functionalities through nanoscale interface engineering. The diverse STDP forms of the memristors with different interfaces may play different specific roles in various spike neural networks.

Neuromorphic computing has become an increasingly popular approach for artificial intelligence because it can perform cognitive tasks more efficiently than conventional computers. However, it remains challenging to develop dedicated hardware for artificial neural networks. Here, a simple bilayer spintronic device for hardware implementation of neuromorphic computing is demonstrated. In L11 -CuPt/CoPt bilayer, current-inducted field-free magnetization switching by symmetry-dependent spin-orbit torques shows a unique domain nucleation-dominated magnetization reversal, which is not accessible in conventional bilayers. Gradual domain nucleation creates multiple intermediate magnetization states which form the basis of a sigmoidal neuron. Using the L11 -CuPt/CoPt bilayer as a sigmoidal neuron, the training of a deep learning network to recognize written digits, with a high recognition rate (87.5%) comparable to simulation (87.8%) is further demonstrated. This work offers a new scheme of implementing artificial neural networks by magnetic domain nucleation.

The magnetic Weyl fermion originates from the time reversal symmetry (TRS)-breaking in magnetic crystalline structures, where the topology and magnetism entangle with each other. Therefore, the magnetic Weyl fermion is expected to be effectively tuned by the magnetic field and electrical field, which holds promise for future topologically protected electronics. However, the electrical field control of the magnetic Weyl fermion has rarely been reported, which is prevented by the limited number of identified magnetic Weyl solids. Here, the electric field control of the magnetic Weyl fermion is demonstrated in an epitaxial SrRuO3 (111) thin film. The magnetic Weyl fermion in the SrRuO3 films is indicated by the chiral anomaly induced magnetotransport, and is verified by the observed Weyl nodes in the electronic structures characterized by the angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Through the ionic-liquid gating experiment, the effective manipulation of the Weyl fermion by electric field is demonstrated, in terms of the sign-change of the ordinary Hall effect, the nonmonotonic tuning of the anomalous Hall effect, and the observation of the linear magnetoresistance under proper gating voltages. The work may stimulate the searching and tuning of Weyl fermions in other magnetic materials, which are promising in energy-efficient electronics.

The effects of annealing and magnetic field annealing on the Gilbert damping constant of polycrystalline CoFe thin films were investigated. Angle dependent ferromagnetic resonance (FMR) demonstrates that an in-plane (IP) anisotropy is developed by field annealing which dramatically reduces the effective Gilbert damping constant. An inverse relation between effective IP anisotropic field and effective damping is shown by FMR measurement in cryogenic environment. This relation is further confirmed in bilayer films of IrMn/CoFe where a strong in-plane unidirectional anisotropy is developed. A large effective IP anisotropic field is possibly associated with a smaller distribution of local fields which reduces the FMR linewidths and subsequently effective damping.

The binary alloys with heavy elements have been considered promising candidates for spin-orbit torque application due to the tunable spin Hall effect. In light of previous studies, the effect of crystalline structure on spin Hall effect in nonmagnetic alloys has not been thoroughly studied. Here, we present a systematic investigation of the spin-orbit torques in chemically disordered $\mathrm{C}{\mathrm{u}}_{100\text{\ensuremath{-}}x}\mathrm{P}{\mathrm{t}}_{x}$ and $\mathrm{L}{1}_{1}\text{\ensuremath{-}}\mathrm{C}{\mathrm{u}}_{50}\mathrm{P}{\mathrm{t}}_{50}$ by the spin torque ferromagnetic resonance technique. The results indicate that both the atomic concentration and the degree of the chemical ordering substantially influence the spin-orbit torque efficiency of the CuPt alloys. In chemically disordered $\mathrm{C}{\mathrm{u}}_{100\text{\ensuremath{-}}x}\mathrm{P}{\mathrm{t}}_{x}$, the primary mechanism of spin Hall effect changes from extrinsic to intrinsic when the Pt concentration is increased to larger than $80%$. In $\mathrm{L}{1}_{1}\text{\ensuremath{-}}\mathrm{C}{\mathrm{u}}_{50}\mathrm{P}{\mathrm{t}}_{50}$ with weak chemical ordering, the side-jump and intrinsic mechanisms dominate, whereas the skew scattering mechanism dominates for strong chemical ordering. This work provides a perspective to control the spin-orbit torques in alloys.

The entanglement of charge, spin, orbital and even lattice degrees of freedom in transition metal oxides gives rise to a wide spectrum of exotic properties, like high transition temperature superconductivity and colossal magnetoresistance. The interfaces between these exotic transition metal oxides offer an even more tantalizing platform for the study not only on the fundamental science, but also on potential applications. The LaAlO3/SrTiO3 (LAO/STO) heterostructure is one of the prototypical cases, which exhibits two-dimensional conduction and rich physical properties although both LAO and STO are insulating. In this thesis work, I will present my exploration on the transport properties of such oxide heterostructures synthesized with unit-cell precision by the state-of-the-art pulsed laser deposition (PLD) system. In these experiments, I discussed the mechanism of the insulator-to-metal transition at the heterointerface, confirmed the existence of the Kondo effect at the high carrier density regime and its tunability by gate bias, and explored an alternative way to control the spin-orbit interaction at oxide heterointerfaces. DOCTOR OF PHILOSOPHY (SPMS)

Electronic correlation is believed to play an important role in exotic phenomena such as insulator-metal transition, colossal magnetoresistance, and high-temperature superconductivity in correlated electron systems. Recently, it has been shown that electronic correlation may also be responsible for the formation of unconventional plasmons. Herewith, using a combination of angle-dependent spectroscopic ellipsometry, angle resolved photoemission spectroscopy, and Hall measurements, all as a function of temperature supported by first-principles calculations, the existence of low-loss high-energy correlated plasmons accompanied by spectral weight transfer, a fingerprint of electronic correlation, in topological insulator ${(\mathrm{B}{\mathrm{i}}_{0.8}\mathrm{S}{\mathrm{b}}_{0.2})}_{2}\mathrm{S}{\mathrm{e}}_{3}$ is revealed. Upon cooling, the density of free charge carriers in the surface states decreases whereas that in the bulk states increases, and the recently reported correlated plasmons are key to explaining this phenomenon. Our result shows the importance of electronic correlation in determining correlated plasmons and opens an alternative path in engineering plasmonic-based topologically insulating devices.

Topologically protected magnetic states have a variety of potential applications in future spintronics owing to their nanoscale size (